The present invention relates to a sensor system and method for detecting electric arcs and, more specifically, to a low cost, small and fast response sensor capable of detecting the leading edge of the pressure wave generated by a high power electric arc.
Air around high power electric arcs is rapidly heated to over 10,000 degrees. This heat causes the air to expand rapidly. The expanding air creates a shock wave of pressure that emanates from the arc. As a high powered arc moves it pushes plasma and air at velocities measured at over 800 miles per hour which exceeds the speed of sound. It is desirable that the pressure wave be detected on its leading edge while the pressure is still at a low level as these pressures are known to reach levels that have knocked down cement block walls.
While, as noted above, the pressures from the arc can be quite high, the pressure oscillates up and down quite rapidly due to the rapid motion of the arc. Detection of this pressure wave can be used to identify the presence of the arc.
Pressure sensors such as pressure transducers and pressure switches detect pressure due to the motion in a diaphragm. The motion of the diaphragm is a function of the total force on the diaphragm and the flexibility of the diaphragm. The total force on the diaphragm is a function of pressure (pounds per square inch or PSI) times area of the diaphragm. If very low pressures need to be detected then a large area diaphragm is needed to accumulate enough force to cause the diaphragm to move. The use of a large area greatly slows the response time of the pressure sensor. Thus, if the pressure sensor diaphragm is made large enough to detect the low pressure leading edge of the arc pressure wave, it may incur so much inertia that it will not respond to the rapidly varying arc pressure.
Some of the arc fault detection systems presently on the market open breakers based solely on the light from the arc. Unfortunately, flashlights and strobe lights can also set off photo detectors. An arc flash pressure sensor used in conjunction with arc light sensors provides a more robust arc detection system preventing false alarms from opening breakers and the loss of power at inopportune times.
What is needed then is a low cost, small, fast response pressure sensor capable of detecting the leading edge of the arc-generated pressure wave.